Conjugated polymers are of great interest for the development of optical and electronic applications. The most investigated conjugated polymers are poly(thiophene) (PT) and poly(p-phenylene vinylene) (PPV). Also poly(2,5-thienylene vinylene) (PTV) has attracted great attention because of its high electrical conductivity upon doping and its possible application as a semiconductor in all-polymer field effect transistors. Additionally, PTV is a low band gap semiconductor polymer, which makes it a very interesting material for organic photovoltaic devices.
Several methods have been developed to synthesize PTV. In the early days, PTV was synthesised via the Wessling polymerization method, which is described in U.S. Pat. No. 3,401,152 by R. A. Wessling and R. G. Zimmerman and in J. Polym. Sci.: Polym. Symp. 1985, 72, 55 by R. A. Wessling. The polymerization reaction according to the Wessling method is difficult, because the products tend to form a gel. Moreover, strong acids, which could be toxic, are required during the conversion reaction.
In 1987, Murase et al. and Yamada et al. reported the synthesis of PTV via a precursor polymer with methoxy leaving groups (I. Murase, T. Ohnishi, T. Noguchi, M. Hirooka, Polym. Commun. 1987, 28, 229; S. Yamada, S. Tokito, T. Tsutsui, S. Saito, J. Chem. Soc., Chem. Commun. 1987, 1448). This reaction is an acid catalysed conversion reaction, which is incompatible with device fabrication.
In 1990, Elsenbaumer et al. reported the synthesis and characterisation of PTV and some alkyl-substituted PTV's (R. L. Elsenbaumer, Mol. Cryst. Liq. Cryst 1990, 186, 211). These methods are far from ideal especially for the PTV derivatives due to the relative high reactivity of the monomer and precursor polymer which complicates both monomer and polymer synthesis. The high reactivity is originated from the high electron density of the thiophene ring, which induces a very high instability of the starting monomer when this monomer is reached but generally with low reproducibility and very low yields due to many side-reactions.
This is also the reason why problems occur by using the more recent precursor methods like the sulfinyl route, developed by Vanderzande et al. in 1997 (A. J. J. M. Van Breemen, A. C. J. Issaris, M. M. de Kok, M. J. A. N. Van Der Borght, P. J. Adriaensens, J. M. J. V. Gelan, D. J. M. Vanderzande, Macromolecules 1999, 32, (18), 5728), the bis-xanthate route developed by Son in. 1995 and Burn et al. in 2001 and described in (U.S. patent 1997/5,621,069; European patent EP 0 707 022 A2; S-C. Lo, L.-O. Palsson, M. Kilitziraki, P. L. Burn, I. D. W. Samuel, J. Mater. Chem. 2001, 11, 2228) and the bis-sulfide route developed by Herwig et al in 2003 (U.S. patent 2003/0027963 A1).
To use PTV, other poly(arylene vinylene)s and poly(heteroarylene vinylene) derivatives in plastic electronics, an easy accessible precursor polymer that can be manufactured on a large scale is desirable.